Significance The lack of commercially available HTLV seroconversion panels has made itnecessary to rely on animal models to evaluate antibody development during the course of HTLV infection. These specimens are the only alternative to dilutional samples by which the sensitivity of HTLV screening tests can be judged. Objectives The objectives of this study was to the time course, and sequence of appearance of antibodies against HTLV-1-specific viral antigens in cynomolgus macaques following experimental intravenous inoculation with MT2 cells, an HTLV-I infected persistent cell line. Weekly plasma samples from inoculated animals were tested in a variety of EIA and Immunoblot assays. Results Antibody to p19 was detected as early as week 1 by immunoblot, however , licensed EIA tests based on viral lysate only (week 3) or spiked with recombinant p21e (week 2-3) were less sensitive. No antibody to native env was observed by blots, but antibody against recombinant p21e was detected in both animals at week 2, and against recombinant gp46 was detected in one monkey at week 2 pi. An antibody capture microter plate ELISA that uses recombinant transmembrane env (p21e) and gag (p24) proteins from both HTLV-I and HTLV-II was able to detect antibody at week 1 pi. The increased sensitivity of this new assay was due solely to the p21e antigens and the assay format which can detect both IgG and IgM antibodies. Future Directions Additional studies will be performed to evaluate seroconversion panels generated by experimental inoculation of macaques with HTLV-II. These reagents will used to evaluate commercial diagnostic assays currently in development. KEYWORDS HTLV, antibody